System and method for disinfecting and removing biological material from water to be injected in an underwater injection well

ABSTRACT

A system for disinfecting and removing biological material from water to be injected into an injection well in a water body is described; the system includes: at least one apparatus for the gravitational precipitation of particles from water, which is connected, in terms of fluid, to a source of untreated water and to the injection well; and an apparatus for the addition of an oxidant for the disinfection of water, which is connected in terms of fluid to the apparatus for the gravitational precipitation of particles, a source of untreated water and to the injection well such that the apparatus for the gravitational precipitation of particles is positioned downstream relative to the apparatus for the addition of an oxidant for disinfection. The disclosure also relates to a method for disinfecting and removal of biological material from injection water.

This application is the U.S. National Stage entry under 35 U.S.C. §371of International Patent Application No. PCT/NO2014/050021, filed Feb.11, 2014, and entitled “system and method for disinfecting and removingbiological material from water to be injected in an underwater injectionwell,” which claims priority to Application No. NO20130267, filed Feb.18, 2013, all of which are hereby incorporated by reference in theirentireties for all purposes.

BACKGROUND

The present disclosure relates to a device for disinfecting and removingbiological material from a water flow. More specifically, the disclosurerelates to a system for disinfecting and removing biological materialfrom water to be injected into an underwater injection well, the systemincluding at least one apparatus for the gravitational precipitation ofparticles from the water and at least one apparatus for adding anoxidant to the water, the two apparatuses being connected in terms offluid, and the two apparatuses connecting a source of untreated water toan injection well in terms of fluid. The disclosure also relates to amethod for disinfecting and removing biological material from a waterflow.

It is known to inject water into a petroleum reservoir to increase theproduction rate and the amount of recoverable reserves of the petroleumreservoir. The injection water is carried into the reservoir at apressure which is higher than the in-situ pressure of the reservoir toexpel further hydrocarbons therefrom. Water for injection is usuallytaken from the nearest accessible water source, generally sea water. Seawater contains, inter alia, salts, biological and organic material andother particles which are undesired in the reservoir and in theinjection well with associated equipment. The biological material mayinclude various types of plankton, bacteria and the like, which may havean adverse effect on the well downstream of the point of introduction asit may lead to biological fouling, deposits and/or blocking of equipmentin the well. Biological material may also lead to acidification of thereservoir as sulphate-reducing bacteria may provide good conditions forthe generation of hydrogen sulphide (H₂S). H₂S gas is very toxic andwill lead to considerable challenges for the operation of the system bya break-through into the production well. The H₂S gas may also lead tocorrosion on equipment in the well and in the processing plant fortreating produced hydrocarbons.

From the patent publication WO 2007/035106 A1, an apparatus and a methodfor the non-mechanical separation of particles from a flow of water areknown, the water being carried into a closed space in which the waterflow rate is made sufficiently low for undesired particles to begravitationally precipitated from the water flow.

From the patent publication WO 2004/090284 A1, a device and a method forthe chemical treatment of injection water are known. The injection waterflows through a container containing chemicals in particle, pellet orblock form, whereby the chemicals are dosed gradually into the injectionwater. It is described that the chemical may include at least one ofchlorine, biocide, polyelectrolytes, ferric chloride, deoxidizer,corrosion inhibitor and scale inhibitor.

The patent publication WO 2007/073198 discloses a method and anapparatus for the destruction of organic material in water to beinjected into an injection well. The apparatus includes, among otherthings, an electrolytic cell with associated operational means for thein-situ production of short-lived, free hydroxyl radicals (.OH).

In sum, the above-mentioned patent publications (each of which areincorporated herein in their entireties by reference) describetechniques enabling the cleaning of injection water on a sea floor,wherein undesired particles are disinfected and/or removed from seawater, and wherein cleaned sea water is subsequently used as injectionwater in an injection well completed on the sea floor. The advantages ofbeing able to position a treatment system for injection water on a seafloor are described in the above-mentioned patent publications andinclude, among other things, a reduced need for space, increasedflexibility, reduced need for energy supply and reduced costs.

The apparatus and the method for the gravitational precipitation ofparticles disclosed in the above-mentioned patent publication WO2007/035106 A1 are used today for removing inorganic particles from theinjection water, usually as a first step in a cleaning process. Adrawback of this arrangement is that some biologic material has aspecific gravity that is low and maybe of the same order as the specificgravity of water, so that the biological material will not beprecipitated in the gravitational filtering.

BRIEF SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure relates to a system for disinfectingand removing biological material from water to be injected into aninjection well in a water body, the system comprises: at least oneapparatus for the gravitational precipitation of particles from water,the at least one apparatus for the gravitational precipitation ofparticles being connected, in terms of fluid, to a source of untreatedwater and to the injection well; and at least one apparatus for theaddition of an oxidant for the disinfection of water, the at least oneapparatus for the addition of an oxidant being connected, in terms offluid, to the at least one apparatus for the gravitational precipitationof particles, the source of untreated water and to the injection well,wherein the at least one apparatus for the gravitational precipitationof particles being positioned downstream relative to the apparatus forthe addition of an oxidant for disinfection.

The oxidant may be selected from a group consisting of chlorine,dioxygen, ozone, hydrogen peroxide, hypochlorite, chlorine dioxide andother oxidizing biocides, but the disclosure is not limited thereto.

The oxidant may be added from a solid, semisolid or liquid state or theoxidant may be produced electrolytically.

Tests performed and described herein have shown that the addition of anoxidant to the injection water affects the cell structure of biologicalmaterial in such a way that the cell structure decomposes and thespecific gravity of the biological material increases. The gravitationalprecipitation of biological particles which have a specific gravity thatmakes such precipitation difficult or impossible thus becomes far moreeffective. A further embodiment therefore provides a method ofperforming gravitational filtration of biological material comprising:injecting water comprising chlorine into an injection well; increasing aspecific gravity of the biological material present in the body of waterinjected into said well; and filtering the biological material from thewater comprising said well.

In what follows, the apparatus for adding an oxidant to the injectionwater will be exemplified by an apparatus for adding chlorine to theinjection water, but it is to be understood that the disclosure is notlimited thereto.

In one embodiment, the apparatus for adding chlorine may include acontainer for the addition of chlorine from a solid or semisolid stateto the injection water. For example, it may be in block, powder or gelform. The water is carried through the container in such a way that itgets into contact with chlorine in solid or semisolid from, wherebychlorine is dosed gradually into the injection water.

In one embodiment, the water may be circulated in a circulation circuituntil the water has picked up a desired concentration of chlorine asdescribed in the Norwegian patent NO 324547 (which is incorporatedherein in its entirety by reference).

In one embodiment, the at least one apparatus for the addition ofchlorine may include a device for the electrolytic production ofchlorine. Chlorine may be produced by the electrolysis of sea water andthe apparatus may be an electrolytic cell of a type known per se.

In one embodiment, the at least one apparatus for the addition ofchlorine may include a container for the addition of chlorine from aliquid state. This may be done, for example, by means of a refillable,flexible volumetric storage unit, wherein such containers are describedin the Norwegian patent NO 331478 (which is also incorporated herein inits entirety by reference).

A further advantage of dosing chlorine into the injection water upstreamof the apparatus for the gravitational precipitation of particles isthat the chlorine will have a long detention time in the apparatus forthe gravitational precipitation of particles, and that the chlorine willthereby have sufficient time to complete its reaction with biologicalmaterial in the injection water. In some embodiments, the detention timeof the injection water in the apparatus for the gravitationalprecipitation of particles may be several minutes and even severalhours. The long detention time is distinctive from that of the prior-artwater-treatment plants in which the chlorine has a reaction time whichis often less than one minute. By monitoring the amount of chlorine atthe outlet of the apparatus for the gravitational precipitation ofparticles and controlling the dosing rate of chlorine, it may be ensuredthat all the chlorine will be reacted completely in the apparatus forthe gravitational precipitation of particles.

In one embodiment, the system may include an apparatus provided with afiltering membrane for filtering the injection water downstream of thechlorine addition. Said filtering membrane may, among other things,remove various particles of salts and minerals left in the injectionwater. Chlorine is known to be harmful to filtering membranes, and whensuch membranes are used, the use of chlorine as a disinfectant upstreamof the membranes has been prevented till now. The filtering membranemay, for example, be of a type as described in the Norwegian patentapplication NO 20101192 (which is incorporated herein in its entirety byreference).

In addition, the system may include a device for the electrolyticproduction of free hydroxyl radicals, wherein the device for theelectrolytic production of free hydroxyl radicals may be connected, interms of fluid, to the apparatuses for the gravitational precipitationof particles and addition of chlorine, to the source of untreated waterand to the injection well. Short-lived, free hydroxyl radicals are veryeffective for removing organic material in a water flow. The device forthe electrolytic production of free hydroxyl radicals could thereby helpto further clean the injection water before injection into the injectionwell. The device for the electrolytic production of free hydroxylradicals may be placed downstream relative to the apparatus for thegravitational precipitation of particles.

In addition or as an alternative to the device for the electrolyticproduction of free hydroxyl radicals, the system may include a devicefor the electrolytic production of mixed oxidants. Mixed oxidants may beproduced by the electrolysis of sea water, and the device may be of akind known per se. It has been shown that mixed oxidants are very wellsuited for inactivating various micro-organisms.

In a second aspect, the disclosure relates to a method for disinfectingand removing biological material from water to be injected into aninjection well in a water body, the method including the followingsteps: by means of at least one apparatus for the disinfection of water,adding an oxidant to the injection water; by means of at least oneapparatus for the gravitational precipitation of particles from water,removing particles from the injection water; in terms of fluid,connecting the apparatuses for the gravitational precipitation ofparticles and the addition of an oxidant, to a source of untreated waterand to the injection well, characterized by the method including placingthe apparatus for the gravitational precipitation of particles in waterdownstream relative to the apparatus for the chemical disinfection ofwater.

In what follows, the step of adding an oxidant to the injection waterwill be exemplified by adding chlorine to the injection water, eventhough the disclosure is not limited thereto.

In one embodiment, the step of adding chlorine to the injection watermay include adding chlorine from a solid or semisolid state.

In one embodiment, the step of adding chlorine to the injection watermay include producing chlorine by means of an electrolytic cell.

In one embodiment, the step of adding chlorine to the injection watermay include adding chlorine from a liquid state.

The method may further include providing the system with a device forthe electrolytic production of free hydroxyl radicals, and, in terms offluid, connecting the device for the production of free hydroxylradicals to the apparatuses for the addition of chlorine andgravitational precipitation of particles, to the source of untreatedwater and to the injection well.

The method may further include providing the system with a device forthe electrolytic production of mixed oxidants and, in terms of fluid,connecting the device for the production of mixed oxidants to theapparatuses for the addition of chlorine and gravitational precipitationof particles, to the source of untreated water and to the injectionwell.

The method may further include filtering the injection water by means ofan apparatus provided with a filtering membrane downstream relative tothe apparatus for the gravitational precipitation of particles, and thusalso downstream relative to the apparatus for adding chlorine to theinjection water.

In a third aspect, the disclosure relates to the use of chlorine toincrease the specific gravity of biological material in water to beinjected into an injection well in a water body.

BRIEF DESCRIPTION OF THE DRAWINGS

In what follows, exemplary embodiments are described with reference tothe accompanying drawings, in which:

FIG. 1 shows a first embodiment of the present disclosure viewed fromabove;

FIG. 2 shows a second embodiment of the present disclosure viewed fromabove;

FIG. 3 shows a third embodiment of the present disclosure viewed fromabove; and

FIG. 4 shows a fourth embodiment of the present disclosure viewed fromabove.

In what follows, the reference numeral 1 indicates a system inaccordance with the present disclosure. The figures are shown in aschematic and simplified manner and elements which are not central tothe disclosure and/or elements that, to a person skilled in the art,will be known parts of the system may have been omitted from the figuresfor clarity and conciseness. In the figures, the direction of the waterflow is indicated by straight arrows.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a first embodiment of the present disclosure. The system 1is placed on a sea floor in a water body 2 in the vicinity of a platform5. Untreated sea water is guided into a water-intake device 14, thewater-intake device 14 being connected to a coupling device 51 on theplatform 5 via a control cable 52. The control cable 52 deliverselectric power and/or communication signals to and/or from thewater-intake device 14. Various valves and pumps for controlling theintake and outlet of water into and from the water-intake device 14 arenot shown. Said intake and outlet can be controlled by means of acontrol unit, not shown, placed on the platform 5 and/or at thewater-intake device 14 on the sea floor.

In the water-intake device 14, the untreated sea water is furthersupplied with chlorous water from a container 13, which adds chlorinefrom a liquid state to the injection water. In the exemplary embodimentshown, the container 13 is arranged as a refillable, volumetric,flexible storage tank as described in the Norwegian patent NO 331478.The container 13 is connected to the coupling device 51 of the platform5 via a control cable 54. Valves and pumps, not shown, for dosing liquidchlorine into the sea water in the water-intake device 14 may thereby becontrolled by means of a control unit not shown. The control unit, notshown, may be on the platform 5 and/or on the sea floor together withthe container 13. The container 13 is further provided with a valve, notshown, for refilling chlorine from an external source not shown, asdescribed in said Norwegian patent NO 331478. Said valves of thecontainer 13 may further have been placed in signal communication with asensor, not shown, for measuring the chlorine content of the water, sothat a desired amount of chlorine may be maintained in the water.

The chlorinated water is further carried through a supply line 18 intoan apparatus 12 for the gravitational precipitation of particles. Theapparatus 12 is shown in the form of a container which is known from thepatent publication WO 2007/035106 A1. The chlorinated sea water iscarried into the container 12 via an inlet, not shown, and is allowed toflow slowly towards an outlet, not shown, of the container 12. The flowrate in the container 12 is sufficiently low for particles of a greaterspecific weight than water to settle onto the bottom of the container12. According to the prior art, it has been difficult to precipitatebiological material in such a container 12 because of the biologicalmaterial basically having a specific gravity which is of the same orderas that of the sea water which is to be cleaned. According to thepresent disclosure, the sea water is chlorinated upstream of thecontainer 12, whereby the cell structure of the biological material inthe water collapses and the specific gravity of the biological materialincreases. Thereby the gravitational precipitation of biologicalmaterial becomes far more effective. The time it takes from when thewater is carried into said inlet of the container 12 until it leaves thecontainer 12 from said outlet may generally be in the order of 30minutes and up to one hour and, in some embodiments, up to severalhours. The container 12 for the gravitational precipitation of particlesis connected to the platform 5 via a control cable 55. Electric powerand communication signals transferred via the control cable 55 may beused for controlling valves and pumps, not shown, connected to thecontainer 12 for the gravitational precipitation of particles by meansof a control unit not shown. The control unit may be the same as thatmentioned above, or it may be a separate control unit.

From the container 12 for the gravitational precipitation of particles,the water is carried through the supply line 18 to a high-pressureinjection pump 31 and further into an injection well 3. The injectionpump 31 is connected to the coupling device 51 of the platform 5 via acontrol cable 57, and the injection pump 31 may be controlled by meansof a control unit not shown.

FIG. 2 shows an alternative embodiment of the present disclosure. Anapparatus 13′ for the addition of chlorine to the injection water isprovided as an electrolytic cell, hereinafter referred to as a chlorinecell 13′. The chlorine cell 13′ is connected to the coupling device 51of the platform 5 via the control cable 54. The amount of sea watercarried into and out of the chlorine cell 13′ can thereby be controlledby means of valves and pumps, not shown. Chlorous water is carried fromthe chlorine cell 13′ via a dosage line 19 into the water-intake device14 in the same way as that mentioned above.

Downstream of the apparatus 12 for the gravitational precipitation ofparticles, the system 1 in the embodiment shown in FIG. 2 is furtherprovided with an apparatus 15 for the electrolytic production of freehydroxyl radicals, referred to, in what follows, as the hydroxyl cell15. The hydroxyl cell 15 is connected to the coupling device 51 of theplatform 5 via a control cable 56, whereby the amount of water enteringand exiting the hydroxyl cell 15 via the supply line 18 may becontrolled by means of valves and pumps, not shown, connected to acontrol unit not shown. The cleaned water is carried onwards to theinjection pump 31 and into the injection well 3.

In FIG. 3, yet another alternative embodiment of the present disclosureis shown. Here, an apparatus 13″ for the addition of chlorine to theinjection water is provided as a container 13″ for dosing chlorine froma solid or semisolid state. Untreated sea water is carried into thecontainer 13″ so that the sea water gets into contact with chlorine in asolid or semisolid state, whereby chlorine is dosed gradually into theinjection water. The apparatus 13″ for dosing chlorine from a solid orsemisolid state into the injection water is connected to the couplingdevice 51 of the platform 5 via the control cable 54 in the same way asthat mentioned above. Pumps and valves, not shown, may be controlled bya control unit not shown.

Downstream of the apparatus 12 for the gravitational precipitation ofparticles from the injection water, the system 1 in the embodiment shownin FIG. 3 is provided with an apparatus 17 for the electrolyticproduction of mixed oxidants, referred to, in what follows, as theoxidant cell 17. The oxidant cell 17 is connected to the coupling device51 of the platform 5 via the control cable 56, and the amount of waterentering and exiting the oxidant cell 17 may thereby be controlled in amanner corresponding to that described above.

FIG. 4 shows a further embodiment of the present disclosure. The entirestream of injection water is carried directly into a chlorine cell 13″.The chlorinated water is carried onwards to the apparatus 12 for thegravitational precipitation of particles. By means of sensors not shown,it will be possible to keep control of the chlorine content of the waterat both the inlet and the outlet of the apparatus 12 for thegravitational precipitation of particles. The amount of chlorine that isdosed into the injection water may thus be small enough for all thechlorine to have time to react completely. The injection waterdownstream of the apparatus 12 for the gravitational precipitation ofparticles will thereby be free of chlorine. The hydroxyl cell 15 will beable to eliminate what might be left of biological material in theinjection water flow in case the amount of added chlorine should be toosmall. In the embodiment shown, the system is further provided withapparatus 16 provided with a filtering membrane for removing anyremaining particles of different salts and minerals in the injectionwater flow. The filtering membrane, which would have been damaged bychlorous water, may be of a type as described in the Norwegian patentapplication NO 20101192.

It will be understood that apparatuses included in the variousembodiments may be combined into further embodiments not shown.

The different control cables 52, 54, 55, 56, 57, 58 are arranged totransfer electric power and/or communication signals to theabove-mentioned different apparatuses connected to the system 1. Controlunits, not shown, for controlling said valves and pumps, not shown,connected to the different apparatuses may be placed on the platformand/or on the sea floor at the different apparatuses. The control cables52, 54, 55, 56, 57, 58 may be arranged for two-way communication, sothat information on the state of the system 1 may also be fed back tothe platform 5.

The system 1 may be provided with a great number of couplings, valves,pumps, sensors and so on, which will be known to a person skilled in theart, therefore variations of the above embodiments will be apparent tothe skilled person. Embodiments of the present disclosure have beendescribed with particular reference to the examples illustrated. Whilespecific examples are shown in the drawings and are herein described indetail, it should be understood, however, that the drawings and detaileddescription are not intended to limit the disclosure to the particularform disclosed. It will be appreciated that variations and modificationsmay be made to the examples described within the scope of the presentdisclosure.

1. A system for disinfecting and removing biological material from waterto be injected into an injection well in a water body, the systemcomprising: at least one apparatus for gravitational precipitation ofparticles from water, wherein the at least one apparatus for thegravitational precipitation of particles being connected, in terms offluid, to a source of untreated water and to the injection well; and atleast one apparatus for the addition of an oxidant for disinfection ofwater, the at least one apparatus for the addition of an oxidant beingconnected, in terms of fluid, to the apparatus for the gravitationalprecipitation of particles, the source of untreated water and to theinjection well, wherein the apparatus for the gravitationalprecipitation of particles is positioned downstream relative to theapparatus for the addition of an oxidant for disinfection.
 2. The systemof claim 1, wherein the at least one apparatus for the addition of anoxidant is an apparatus for the addition of chlorine.
 3. The system ofclaim 2, wherein the at least one apparatus for the addition of chlorineto the water includes a container comprising chlorine in a solid orsemisolid state.
 4. The system of claim 2 or 3, wherein the at least oneapparatus for the addition of chlorine includes a device for theelectrolytic production of chlorine.
 5. The system of claim 2, whereinthe at least one apparatus for the addition of chlorine comprises acontainer for the addition of chlorine from a liquid state.
 6. Thesystem of claim 2, wherein the system further comprises a device for theelectrolytic production of free hydroxyl radicals, wherein the device isconnected in terms of fluid, to the apparatus for the gravitationalprecipitation of particles and the apparatus for the addition ofchlorine to the source of untreated water and to the injection well. 7.The system of claim 2, wherein the system further comprises an apparatuswherein said apparatus comprises a filtering membrane positioneddownstream relative to the apparatus for the gravitational precipitationof particles and downstream relative to the apparatus for the additionof chlorine.
 8. The system of claim 2, wherein the system furthercomprises a device for the production of mixed oxidants, wherein thedevice for the production of mixed oxidants is connected, in terms offluid, to the apparatus for the gravitational precipitation of particlesand to the apparatus for the addition of chlorine, to the source ofuntreated water and to the injection well.
 9. A method for disinfectingand removing biological material from water to be injected into aninjection well in a water body, the method comprising: by means of atleast one apparatus for disinfecting water, adding an oxidant to theinjection water; by means of at least one apparatus for thegravitational precipitation of particles from water, removing particlesfrom the injection water; in terms of fluid, connecting the apparatusesfor the gravitational precipitation of particles and addition ofchlorine to a source of untreated water and to the injection well,wherein the method includes placing the apparatus for the gravitationalprecipitation of particles in water downstream relative to the apparatusfor the chemical disinfection of water.
 10. The method of claim 9,wherein adding an oxidant to the injection water includes addingchlorine to the injection water.
 11. The method of claim 10, whereinadding chlorine to the injection water includes adding chlorine from asolid or semisolid state.
 12. The method of claim 10 or 11, whereinadding chlorine to the injection water comprises producing chlorine bymeans of an electrolytic cell.
 13. The method of claim 10, whereinadding chlorine to the injection water includes adding chlorine from aliquid state.
 14. The method of claim 10, further comprising providingthe system with a device for the electrolytic production of freehydroxyl radicals and, in terms of fluid, connecting the device for theproduction of free hydroxyl radicals to the apparatus for the additionof chlorine and the apparatus for gravitational precipitation, to thesource of untreated water and to the injection well.
 15. The method inof claim 10, wherein the method further includes providing the systemwith a device for the electrolytic production of mixed oxidants and, interms of fluid, connecting the device for the production of mixedoxidants to the apparatuses for the addition of chlorine andgravitational precipitation, to the source of untreated water and to theinjection well.
 16. The method of claim 10, further comprising filteringthe injection water by means of an apparatus provided with a filteringmembrane downstream relative to the apparatus for the gravitationalprecipitation of particles, and downstream relative to the apparatus foradding chlorine to the injection water.
 17. (canceled)
 18. A method ofperforming gravitational filtration of biological material comprising:injecting water into an injection well, wherein the water compriseschlorine; increasing a specific gravity of the biological materialpresent in the body of water injected into said well; and filtering thebiological material from the water comprising said well.